The present invention is directed generally to a liquid dispensing apparatus and method and, more particularly, to a device and method capable of dispensing a controlled volume of an additive liquid into a reservoir liquid.
There are a variety of applications which require some form of device or apparatus that is capable of dispensing a first liquid into a second reservoir liquid. Examples of such applications include chemical processes, plating processes, fertilizer and food processing, and a wide variety of other liquid metering applications. One particularly desirable use of such a dispensing apparatus is to dispense a liquid cleaner into a toilet bowl.
Various prior art liquid dispensers have been widely used for dispensing liquid toilet bowl cleaner. The most commercially successful dispensing containers use a float valve which opens and closes with changes in the toilet tank level during a flush cycle. These dispensers are designed to fill a small receptacle on the top of a float during the fall in the tank water level and then, during the rise in tank water level, to displace the cleaner liquid from the receptacle and into the tank. Problems exist with this method and its implementation. For example, the method is very inefficient. The objective, of course, is to keep the toilet bowl clean, not the water holding tank. Since all the cleaner is dispensed into the tank, rather than the bowl, most of it is flushed down the drain without cleaning the bowl at all. Due to loss down the drain, less than 10% of the cleaner liquid actually is retained in the bowl. Even solid bowl cleaners, which slowly dissolve in the holding tank, share the same inefficient performance as the liquids, since 90% or more is flushed down the drain without doing any substantial cleaning. The prior art float dispenser apparatus are also susceptible to variations in performance. Surface tension, foaming, and dimensional variations can cause complete blockage of the system or great variations in the amount of cleaner dispensed. Because of the significant variation that occurs, it is also difficult to apply such apparatus to the dispensing of small volumes. Most liquid toilet bowl cleaners are formulated to be dispensed in one milliliter quantities. This requires a 12 oz. bottle to provide enough liquid for 350 flushes, or about one month's typical usage. The size of the 12 oz. container is too large to fit in many toilet tanks limiting the use of the product.
Other prior art dispensing apparatus have been tried, but all are either incapable of dispensing accurately the small volume of liquid required, or they are incapable of dispensing during the time period required for most efficient operation. For example, U.S. Pat. No. 1,728,737 to Stoner; U.S. Pat. No. 1,213,978 to Thornton; U.K. Patent No. 8621 and French Patent 2,613,743 all disclose a container of liquid mounted above the tank level with a vent tube extending down below tank level. When the tank level is dropped, air is allowed to enter the container, enabling liquid additive to drain out of the container. These systems have proved impractical because they either dispensed too great a volume (e.g., the '978 Thornton, '621 Great Britain and '743 French patents) and/or they dispensed at an inappropriate time in the flush cycle (all cited patents). This inefficiency was due to the necessary use in the prior art of a vent tube large enough in diameter to empty itself of water as the tank level dropped, thereby allowing air to enter the container through the vent tube. The large diameter vent tube results in a large dispensed volume of additive because water moving inside the vent tube displaces an equal volume of additive from the container. If the vent tube penetrates the tank level a substantial amount (for the purpose of delaying the onset of dispensing), this results in a relatively large volume of water inside the vent tube. If the vent tube is adjusted so that its lowest portion just contacts the water at its highest level, then dispensing begins immediately upon commencement of the flush cycle, wasting considerable additive. In either case, a dip tube vent approach is not satisfactory for dispensing a small controlled volume of liquid.
U.S. Pat. No. 4,507,811 to Buelow, et al. recognized the improved efficiency made possible by dispensing additive into the overflow pipe rather than into the tank. However, the disadvantage of the Buelow device is that it requires toilet tank water to mix with the additive. In Buelow, solid cakes are dissolved to a saturated solution and dispensed in a pre-set amount. However, if a liquid additive, rather than a solid were used, the additive would be continually diluted with each flush. The Buelow device is therefore insufficiently accurate for dispensing small controlled volumes of liquid additives. The Buelow device also has the disadvantage that it must be mounted below the tank waterline. The Buelow dispenser is therefore impractical for use in many installations in which the flushing mechanism would interfere with the mounting of the Buelow device. The dissolving of solids has the inherent disadvantage of being time dependent. A second flush cycle may occur too fast to allow sufficient time for the solution to become saturated, thereby resulting in inadequate cleaner concentration in the bowl.
In still another prior art device, U.S. Pat. No. 1,623,132 to Pennell, et al., the change in one reservoir level is used to control the dispensing of a liquid additive into the same reservoir. Pennell's device is complicated in that it uses an inverted U-tube as a level sensing tube in order to block air from entering the additive container. This U-tube is filled with liquid, allowing a pressure balance condition to develop to prevent liquid from draining out of the additive container. A disadvantage to the Pennell design is that the end of the U-tube is situated directly below the discharge nozzle so that when the container is inverted upon installation, the liquid discharged through the nozzle will fill the U-tube and establish the pressure balance. If the U-tube is not aligned with the nozzle, the entire contents of the container will run out. Thus, the Pennell device dispenses additive into the same reservoir as the controlling liquid, i.e., the tank, rather than into an overflow tank.
Overflow mounting is practical only if the container is very small. Since at least a one month's supply is needed in a practical toilet bowl cleaner container, the amount dispensed each cycle must be very small. A practical overflow mounted dispenser is limited to about 3 ounces in volume. For a month's service, this requires a dispensed volume of about 0.25 ml per cycle, or about 5 drops of liquid. It is critical therefore that this small volume be dispensed at the proper time in the cycle, or it may fail to be adequately mixed with the bowl water. There is a fairly limited combination of dimensions that will dispense the proper amount at the right time. It has been determined that the dispensed volume and timing are significantly affected by the maximum water level, which can vary from one installation to another. It is desirable that these variations do not significantly affect the amount dispensed and it is desirable to have a container that does not need to be adjusted in any way upon installation.
There exists, therefore, a need in the art for a more efficient and effective apparatus and method for dispensing a small, accurately controlled volume of liquid into another liquid reservoir and particularly for dispensing a small volume of liquid toilet bowl cleaner directly into a toilet bowl. For greatest utility, such an apparatus must be small enough to be mounted directly onto the overflow pipe.